Method of heat treatment in carbonaceous atmospheres



Patented Oct. 6, 1936 UNITED STATES PATENT OFFICE DIETHOD OF HEAT TREATMENT IN CARBONACEOUS ATMOSPHERES Pennsylvania No Drawing.

10 Claims.

. Our invention relates to a method of heattreatment of iron, steel, and the like, in a carbonaceous atmosphere.

In accordance with our invention at elevated temperature, is in contact in a chamber with an atmosphere consisting substantially of the gaseous products carbon monoxide, methane and hydrogen derived from a compound, or mixture of compounds, consisting of those stoichiometric compositions of carbon, oxygen and hydrogen, preferably liquid at usual atmospheric temperatures and pressures, which have the here inafter described relations of carbon atoms to oxygen atoms, and which by pyrolytic breakdown yield the aforesaid gaseous products.

In accordance with our method the heat treatment may be rapid, without substantial deposit on the work or within the treating system of soot, or of tarry or hard carbonaceous material.

Our invention further resides in the methods having the characteristics and features hereinafter described and claimed.

Carburizing with compounds such as methane (CH4), ethane -(CH3CH3*), propane (CH 3CH2CH3) butane, and their derivatives, is unsatisfactory because of excessive deposit of soot, orfree carbon, on the work. Attempts have been made to overcome this disadvantage by mixing air with these gases but, in practice, it has been found dificult to obtain and maintain the proper proportions. The apparatus for mixing. is expensive, difiicult to adjust, and will not maintain the critical ratio of gas and air without frequent readjustment. If too much air, or oxygen in other form, is added, the carburizing efiiciency is low, whereas, if too little air is added, soot is deposited. Aside from the difficulty of obtaining the correct proportions of the gases, there is always present the danger of the proportions becoming such that the mixture is explosive;

the metal, 7

Application October 31, 1933, Serial No. 696,020

Liquid compounds, such as benzene and tetrahydronaphthalene, used in carburizing prior to our invention, have also proved unsatisfactory. In general, their use has resulted in heavy deposits of carbon or tar on the work which, in 5 some cases, is so tenacious as to require sandblasting for removal. In addition, the deposited coating is usually so impervious to the carburizing gas that the work is poorly carburized, due to scant and non-uniform transfer of carbon to 10 the work. Theoretically, it would appear that these compounds would afford a high concentration of nascent carbon, but such is not actually the case as their pyrolytic decompositionis not a simple one. On the contrary, the products of 15 decomposition of such compounds polymerize, as evidenced by the formation of naphthalene and tar during the carburizing process.

After extensive research, we have found that high carburizing eificiency and freedom from 20 hard or tarry deposits is readily obtainable by using hydrocarbon compounds which contain oxygen and, provided that if in the molecule there are more than five carbon atoms, there shall not be more than five carbon atoms in series unless interrupted or bridged by an oxygen atom.

Fusel oil, a mixture of iso-butylcarbinol, having the molecular formula has proved satisfactory, aflording rapid carburization and freedom from tarry deposits or excess soot. As shown by their formulae, the molecule of each of these compounds contains oxygen. The products of the pyrolytic breakdown of fusel oil and of the other compounds selected in accordance with our invention are substantially solely the gases carbon monoxide, methane and hydrogen. Presumably, the oxygen combines in the last stage of the pyrolytic breakdown of the fusel oil with the carbon (which latter would otherwise be deposited as soot) forming carbon monoxide which, in turn, yields nascent carbon which enters into the carburizing reaction, the carbon combining with or going into the iron or steel under treatment. The liberated oxygen combines with another carbon monoxide molecule, forming carbon dioxide which, in turn, reacts with any carbon that may have been deposited on the Work, again forming carbon monoxide, so keeping the surface 'of the metal clean and receptive to carburizing.

Since the oxygen is in the molecule of the components of the carburizing mixture, its proportion is definitely fixed by chemical laws, or

stoichiometrically, avoiding the difficulty, en-

countered in gas carburizing with propane, butane, or the like, of need continuously to add the proper amount of air or oxygen and, in accordance with our invention, polymerization does not .HHHHHHHHHHHHHHHHH A A A A A A A A Though both fusel oil and oleic acid contain oxygen, fusel oil, made up of short carbon chain compounds, is well suited. for our carburizing method, whereas oleic acid, having a long carbon chain uninterrupted by one or more atoms of oxygen, lacks the advantages of our materials. Use of oleic acid, as above stated, results in formation of heavy carbon cake on the work. In addition, its time of pyrolytic breakdown is too slow. It is necessary or desirable that the carburizing gas be rapidly circulated or forcibly stirred for efficient and uniform carbirrizing. It is, therefore, quite essential, fronina practical standpoint, to utilize the compound whose time of pyrolytic breakdown is short. Linolic acid (CmHazOz) and palmitic acid (C1eH32O2) are also unsuited because having long carbon chans uninterrupted by an oxygen atom.

Diethyleneglycol, ethylacetate and ethyleneglycolmonoethylether, which are liquids at atmospheric pressure and ordinary temperatures, we

have also found to be well suited for carburizing;

all contain oxygen, ensuring freedom from excessive soot deposits. The molecular formulae for these compounds are I Diethyleneglycolmonoethylether, commercially known as Carbitol, a liquid at ordinary atmospheric pressure and temperature, has also been found well suited for carburizing. As shown by molecular formula,

from the closed chain or cyclic type, such as, for

example, benzene, whose molecular formula is We have found that cyclic compounds, when having an uninterrupted loop of carbon atoms in series, are unsuited for jcarburizing because they polymerize, forming tarry compounds which are deposited on the work and preclude satisfactory caburizing. When, however, there is at least one atom of oxygen included in the closed chain, as in furfural, whose molecular formula is polymerization does not occurand the oxygen prevents excess deposit of soot during pyrolytic breakdown.

In general, we have found that'superior carburizing, characterized by rapid reaction of the carburizing gases withthe metal, and freedom from formation on the work of excessive soot and/or coke, hard, caked carbon or tarry deposits, can be effected by using compounds of oxygen, carbon, and hydrogen with not more than five carbon atoms in an open or closed chain, unless bridged or interrupted by an oxygenatom. The foregoing compounds have been selected as representative of this class.v a

In general, our carburizing agent consists of a compound, or mixture of compounds, of oxygen, carbon and hydrogen whose molecule has a ring sequence, or a chain sequence, of carbon atoms not more than five in number unless interrupted or bridged, as in furfural, by at least one oxygen atom.

Preferably, the carburlzing compound should be liquid at ordinary room temperatures, at atmospheric'pressura'because of the greater sin!- plicity of controlling the rate of feed. However,

many solids as citric acid, crotonic acid, ethyl malonic acid, glutaric acid, maleic acid, etc., come a hydrocarbon, lacking or deficient in oxygen,-

with a compound of oxygen, carbon and hydrogen; for example, hexane and/or pentane; whose molecules contain no oxygen, may be mixed with erythritol and/or glycerol to form a suitable carburizing mixture, liquid under atmospheric conditions.

We prefer, however, to use fusel oil, carbitol or diethyleneglycol because of their cheapness, low vapor pressure, low boiling point, and high flash temperature. In general, the'vapor pressure of the liquid selected should not materially exceed about mm. of mercury at 20", nor should the flash point be less than about 100 C. Otherwise, there is some danger from inflammable vapors external to the furnace.

While various types of furnaces may be used for carburizing or heat-treating metals by compounds of the class comprised by our invention, it is preferable or desirable to use a furnace of the type in which the carbonaceous atmosphere is forcibly circulated and forcibly stirred in contact with the work, as by a fan.

Preferably, the carbonaceous liquid is fed to a furnace passage or chamber in the form of fine mist or spray at suitably high pressure, for example, of the order of 2500 pounds per square inch, as by an atomiz'ing nozzle.

For carburizing the temperature, in accordance with usual practice, is maintained at about 1700 F.

By use of compounds of the character specified, there are no substantial deposits of soot, or of hard or tarry carbonaceous materials, either upon the work or upon the interior structure of the furnace exposed to the carbonaceous atmosphere.

By way of illustration, the procedure and results of a typical run are briefly given. About 150 pounds of cylindrical specimens of S. A. E. 1020 steel, 7 inch in diameter and 6 inches long were disposed haphazard in the work-container of a carburizing furnace of the type in which the carbonaceous atmosphere is forcibly stirred in contact with the work and circulated by a fan. The temperature was maintained at 1700 F. After a preliminary furnace-flushing period of about fifty minutes, the carburizing agent, fusel oil, was fed as liquid at the rate of 450 cubic centimeters per hour for two hours. The results were as follows:

Case Depthin inches Hyper-eutectoid 0.012

utectoid 0.009

Hypo-eutectoid 0. 009

Total 0. 030

On removal of the specimens, there was no deposit of carbon or soot, or other carbonaceous material adherent to or caked upon any of them.

Use of nitrobenzene or bone oil produces excessive deposits on the surface of the work and in the furnace, and we hereby disclaim their use for carburizing or heat-treatment.

What we claim is:

1. The method of heat-treating metal which comprises heating the metalin a chamber to heat-treating temperature, providing in said chamber a carbonaceous'atmosphere consisting substantially of the gaseous products carbon monoxide, methane and hydrogen, and providing said products in said atmosphere by pyrolytical- 1y breaking down a compound, or mixture of compounds, consisting of stoichiometric composition of carbon, oxygen and hydrogen, characterized by a sequence of carbon atoms not more than five in number unless bridged or interrupted by an atom of oxygen, and which when pyrolytically broken down to effect the aforesaid gaseous products yields substantially no deposit of soot or of tarry or hard carbonaceous material.

2. The method of heat-treating metal which comprises heating the metal in a chamber to heat-treating temperature, providing in said chamber a carbonaceous atmosphere consisting substantially of gaseous products of definite compositions, and providing said products in said atmosphere by pyrolytically breaking. down a compound, or mixture of compounds, consisting of stoichiometric composition of carbon, oxygen and hydrogen, characterized by a sequence of carbon atoms-not more than five in number unless bridged or interrupted by an atom of oxygen,

and which when pyrolytically broken down to effect the aforesaid gaseous products of definite compositions yields substantially no deposit of soot or of tarry or hard carbonaceous material.

3. The method of carburizing metal which comprises heating the metal in a chamber to carburizing temperature, providing in said chamber a carbonaceous atmosphere consisting substantially of gaseous products of definite compositions,

and providing said products in said atmosphere bypyrolytically breaking down a compound, or mixture of compounds, consisting of stoichiometric composition of oxygen, carbon and hydrogen, characterized by a sequence of carbon atoms not more than five in number unless bridged or interrupted by an atom of oxygen, and which when pyrolytically broken down to effect the aforesaid gaseous products of definite composition yields substantially no deposit of soot or of tarry or hard carbonaceous material.

4. The method of carburizing metal which comprises heating the metal in a chamber to'carburizing temperature, providing in said chamber a carbonaceous atmosphere consisting substantially of gaseous products of definite compositions, and providing said products in said chamber by pyrolytically breaking down a mixture of isobutylcarbinol and secondary butylcarbinol.

5. The method of carburizing metal which comprises heating the metal in a chamber to carburizing temperature, providing in said chamber a carbonaceous atmosphere consisting substantially of gaseous products of definite compositions,

and providing said products in said chamber by pyrolytically breaking down the compound diethyleneglycol.

6. The method of carburizing metal which comprises heating the metal in a chamber to carburizing temperature, providing in said chamber a carbonaceous atmosphere consisting substantially of gaseous products of definite compositions,

.and providing said products in said chamber by pyrolytically breaking down the compound diethyleneglycolmonoethylether.

7. The method of heat-treating metal which comprises heating the metal in a chamber, providing in said chamber a carbonaceous atmosphere consisting substantially of gaseous prodnets of definite compositions, and providing said products in said chamber by pyrolytically breaking down a compound, or mixture of compounds, selected from the group consisting of fusel oil, diethyleneglycol, diethyleneglycolmonoethylether,

furfural.

8. In the art of heat-treating metal at elevated temperature in the presence of a carbonaceous atmosphere, the method which comprises constituting the atmosphere substantially of those gases of definite composition resulting from pyrolytic breakdown of a mixture of isobutylcarbinol and'secondary butylcarbinol.

s 9. In the art of heat-treating metal at elevated temperature in the presence of a carbonaceous atmosphere, the method which comprises constitutethyleneglycolmonoethylether, ethyl acetate, and

ing the atmosphere substantially of those gases of definite composition resulting from pyrolytic breakdown of the compound diethyieneglycol.

10. In the art of heat-treating metal at elevated temperature in the presence of a carbonaceous atmosphere, the method which comprises constituting the atmosphere substantially of those gases of definite composition resulting from pyrolytic breakdown of the compound diethyleneglycolmonoethylether.

FRITZ EBERLE.

\ CRANDALL Z. ROSECRANS. 

